Method and device for minimizing stitching faults in embroidering devices

ABSTRACT

A method and the device for minimizing stitching faults in embroidery devices ( 1 ) is provided, which includes a drive for moving the material holder ( 13 ), with an article to be sewn ( 11 ) being stretched therein, based on the knowledge that such stitching faults frequently can be explained by oscillations of the article to be sewn ( 11 ) and the material holder ( 13 ) due to rapid accelerations. Various effects, such as different types of articles to be sewn, changing weights, and friction ratios can cause a change of the oscillation behavior. One or more sensors ( 29, 43, 44 ) are provided and arranged such that they can detect the oscillation of the article to be sewn ( 11 ) and/or the material holder ( 13 ). The control of the drive and/or the sewing needle ( 23 ) occurs depending on the detected oscillations such that deviations of the stitching site from the predetermined target value is minimized.

BACKGROUND

The invention is directed to a method and a device for minimizing stitching faults in embroidering devices.

In embroidering devices, such as e.g., embroidering machines or sewing machines with an attachable embroidering module, the article to be embroidered is stretched into a frame. The device is arranged below the stitch forming device and/or the sewing needle and can be displaced and/or positioned in the sewing plane using a driving device. A control unit controls both the movement of the sewing needle as well as the one of the driving device for the embroidery frame. For each individual stitch, the embroidery frame with the stretched article to be sewn is displaced into the position required, in order for the stitching site of the needle in the article to be sewn to be equivalent to a predetermined target position. Conventionally for this purpose, common x-y-drives with two stepper motors are used, which can be addressed independent from one another. Here, for example, toothed belts can be provided to perform a transfer of the movement from the motors to the corresponding carriage, which can be displaced in a guided manner.

In such conventional embroidery devices the embroidery frame and thus the article to be sewn can be excited into vibrations based on inertia. This particularly applies to high stitch frequencies and/or to fast changes of direction and the rapid accelerations connected therewith. As a consequence, the actual stitching position of the needle in the article to be sewn can deviate from the predetermined target position. When very large forces or accelerations affect the embroidery frame, it can result not only in contouring errors but also in a skipping of individual steps, when stepper motors are used, and thus in permanent contouring errors (until the subsequent reference point is taken for the stepper motors.) Various effects, such as differences in the types of articles to be sewn, the weight to be moved, or the friction ratios result in the fact that the vibration behavior cannot be calculated precisely and thus it cannot be eliminated a priori.

SUMMARY

Therefore, the object of the present invention is to provide a method and a device, by which stitching faults caused by vibrations of the embroidery frame can be minimized in embroidery devices.

This object is attained in a method and a device for minimizing stitching faults in embroidery devices according to the present invention.

According to the invention, sensors are provided, which directly or indirectly detect characteristic features of vibrations of the embroidery frame and/or the article to be sewn stretched therein.

In order to reduce and/or minimize stitching faults, in a preferred embodiment of the invention the drive motor or drive motors for the embroidery frame are controlled such that the amplitudes of the oscillations, namely the vibrations of the embroidery frame developing during the approach of the individual stitching positions caused by the inertia and the accelerations occurring, amount to values below a predetermined minimum. Here, preferably the speed and/or movement progression between the individual stitching positions is optimized and/or controlled or adjusted such that the accelerations developing in the predetermined stitching frequencies each are minimal.

As an alternative to minimizing the vibrations of the frame, the movement of the sewing needle may also be controlled and/or modified such that the stitching time occurs precisely at the time the target position for stitching into the article to be sewn is directly below the sewing needle.

In a further development of this alternative embodiment, the target positions can each be adjusted such that the stitches entering the article to be sewn are each positioned at the inversion points of the oscillating movements detected.

The detection of the oscillations preferably occurs via an optical sensor in proximity of the stitching site of the sewing needle, with the optical sensor being equivalent to a laser mouse sensor, in principle, which detects images of the surface of the article to be sewn with a high spatial and temporal resolution and uses said information to calculate the respective position or speed or acceleration of the article to be sewn. This method is advantageous in that the sensor can also be used for controlling the article to be sewn and/or the movement of said article during the formation of the stitch.

Alternatively, for example, one or more sensors for detecting force or torque can be provided, e.g., in the area of the mounting positions of the embroidery frame at the carriage of the driving device. In this case, the oscillations of the embroidery frame can be deducted from the measured signals of the sensors. Here, those signal components of the measuring signal, that can be purely deducted from the movement predetermined by the control without any elasticity-dependent excessive oscillation components, are filtered out of the measurement signals.

Instead of stepper motors, preferably controllable servomotors can also be used for moving the embroidery frame, with the servomotors comprising, e.g., rotary sensors for detecting the actual rotary position of the motor. The detection of the contouring errors can also be used for analyzing the vibration behavior of the embroidery frame.

Furthermore, it is possible to detect electric measurements, such as e.g., current or voltage consumption of the motor or motors and deduct information therefrom concerning the vibrations of the embroidery frame.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is explained in greater detail using the drawing figures. In the drawings:

FIG. 1 is a side view of an embroidery device, comprising a sewing machine with a coupled embroidery module;

FIG. 2 is a top view of a sewing machine with a coupled embroidery module;

FIG. 3 is a view of a sewing foot, in a partial cross-section, with an integrated optic sensor;

FIG. 4 is a detailed view of the connection point of a embroidery frame with a carriage of an x-y-drive; and

FIG. 5 is a control arrangement diagram with an adaptive control.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, an embroidery device 1 is shown with a stitching module 5 coupled to a sewing machine 3. The embroidery module 5 is connected to the sewing machine 3 via a connection wire 7 (FIG. 2). The power supply of the embroidery module 5 is provided via the connection wire 7, as well as an effective connection of the embroidery module 5 to a sewing machine control 9. The embroidery device 1 can, e.g., also be provided as an embroidery machine with an enlarged support for articles to be sewn and with an integrated x-y-drive (not shown). For the embroidering process, the article to be sewn 11 is stretched in an embroidery frame and/or in a material holding device, in general. Subsequently, the holding device is mounted as stiff as possible to a holder 17, e.g., using a clamp or fastening means 15, in general, with a driving device 18 and/or an x-y-drive allowing the fastener to be moved back and forth in the two directions x and y of the sewing plane.

The driving device 18 comprises a first slide or carriage 19, which can be driven and/or displaced by a motor in the first sewing direction x, and a second slide or carriage 21, which can be driven and/or displaced in a guided manner by a motor in the second sewing direction y in reference to the first carriage 19 (FIG. 2). Preferably, adjustable servomotors are used as the motors (not shown) for the driving device 18. Alternatively, sometimes stepper motors are used as well. In general, the first motor is connected in a fixed manner to the housing of the embroidery module 5 for the movement of the first carriage 19, and the second motor is connected in a fixed manner to the movable first carriage 19 for the movement of the second carriage 21. The transfer of the rotary motion into a linear motion can occur, e.g., via toothed belts 45 (FIG. 4). In general, drives are arranged for adjusting the speeds between the motors and the toothed belt 45. Guidance rods 22 or other guiding devices may be provided for guiding the carriages 19, 21.

A fastener 17 is provided at the second carriage 21, protruding perpendicularly to a direction of movement y. The control 9 of the sewing machine adjusts, among other things, the upward and downward motion of the sewing needle 23, which is held below the machine head 25 at a needle rod 27 that can be driven by a motor, and the movements of the two carriages 19, 21.

An optic sensor 29 is provided at the bottom of the sewing machine head 25, which can detect and/or determine at least two dimensions of the space, and which preferably comprises a micro-camera. The optic sensor 29 is embodied and arranged such that it can detect a surface of the article to be sewn in an area of the stitching site of the needle 23 and/or parts of the material holding device 13. A display optic (not shown), which is located in front of the sensor 29 or is a component of the sensor 29, displays the area of the article 11 to be detected and/or the material holding device 13 onto the light-sensitive sensor area. Preferably, the sensor 29 comprises a light source for lighting the detection area with light in the visible or invisible range of the spectrum. The optic sensor 29 has a high local resolution, amounting approximately to 0.1 mm in two dimensions, and a high temporal resolution and/or scanning rate of 3000 Hz, for example. An image processing unit 30, which e.g. can partially or entirely be integrated in the optic sensor 29 or in the machine control 9 is provided so that it can reliably detect oscillations of the article to be sewn 11 and/or the material fastening device 13, even when the amplitudes of the oscillation are small and the frequency of the oscillation is high.

Alternatively, the optic sensor 29 or parts thereof may also be integrated e.g., in the sewing and/or embroidery foot, which comprises for example an interchangeable sole 32 as shown in FIG. 3. The sensor 29 is shown in a partial cross-section in FIG. 3, so that essential elements on the inside are discernible. The design and operation of the sensor 29 are essentially equivalent to that of sensors used in laser computer mice. Such sensors have been developed, e.g., by the companies Logitech and Agilent, and are used in laser mice under the name “MX1000 cordless Laser Mouse”. A light source 33 in the form of a laser diode emits pulsed laser light. This light is radiated to the surface of the article to be detected via a display optic comprising a prism 35. Using the display optic with the prism 35 and one or more lenses 37, the surface of the article to be sewn, lit by the laser light, is imaged on an image sensor 39. The sharpness of the imaging optic is high enough that the jumping motions of the sewing foot rod (not shown), at which the sewing foot 31 is fastened, developing during the embroidering process do not compromise the safe detection of the article 11 to be sewn. The sensor 29 can detect more than 6000 individual images per second. Using the movement and/or change in location of the structural features of images subsequently following one another, the image processing unit 30 calculates values, which characterize the oscillating behavior of the material 11 to be sewn and/or the material fastening device 13, i.e., for example amplitude, frequency, and direction of oscillation components. For these calculations, advantageously an algorithm is used for a FFT (Fast Fourier Transformation). Alternatively, other calculations can be performed as well in order to yield data typical for the oscillation behavior. In these calculations, the portion of the measurement signals purely deductible from the predetermined target movement and not including any excessive oscillation components are filtered off. In general, sensors with light diodes can also be used as light sources 33 for detecting oscillations, similar to conventional optic mice. The scanning rate ranging from approximately 1000 Hz to 1500 Hz and the resolution of such sensors is at the lower range tolerable for a reliable detection of the oscillation. Better suitable are scanning ranges above 1500 Hz.

The sewing or embroidery foot 31 can be connected to the machine control 9 via a connection wire 41 having a plug 42, as shown in FIG. 3. Alternatively or in additional thereto wireless communication connections (radio, infrared light, etc.) and/or light conductors could be used as well.

Instead or in addition to the optic detection of oscillations of the article 11 to be sewn or the material holding device 13 other physical measurements can also be used to characterize the oscillation behavior. Due to the fact that the cause of such oscillations is based on the acceleration of inert masses and/or the changes of the corresponding speed vectors and the elasticity of the materials used, such vibrations can also be detected indirectly via forces and/or torques. For example, force sensors 43 (FIG. 4) can be arranged in the connection area of the fastener 17 and the material holding device 13, which can detect dynamic pressure and/or tensile forces, preferably independent from their direction, thus for example piezo-elements or strain gauges. The forces measured are proportional in reference to the respective acceleration. When they occur periodically alternating in the opposite direction, the amplitude and frequency of said forces are equivalent to the amplitude and the frequency of the oscillation movement of the material holding device 13.

Pressure, force, or torque sensors 43 can also be mounted at other sites, at which forces equivalent to the vibrations of the material holding device 13 are to be expected, i.e. for example at the toothed belts 45, which transfer the movement of the motors to the carriages 19, 21 or at the encircling wheels for the toothed belts.

In another embodiment, electric measurements, such as e.g., current consumption or motor output, are controlled. Contouring errors and the corresponding forces can be deducted therefrom. In particular, the affecting forces can be determined indirectly and conclusions can be drawn from their cause.

FIG. 4 shows a possible arrangement of force sensors 43 in the area of the connection site of the embroidery frame 13 to the second carriage 21 of the x-y-drive and/or at the connection site of the second carriage 21 with the corresponding toothed belt 45. In FIG. 4, the embroidery frame 13 is shown separated from the carriage 21. The fastening means 15 comprise two guiding grooves 47 and a spring-loaded fixing device 48. When being placed onto the fastener 17, the fixing device 48 is compressed against the effecting spring force. This way, the guiding grooves 47 are released and can be pushed over two holding pins 49 with protruding stops 49 embodied correspondingly. Here, the guiding groove 47 or the spring-loaded bar (not shown) of the fixing device 48 come into contact with the holding pins. Subsequently the fastening device 15 with the embroidery frame 13 is fixed at the fastener 17 in a form-fitting and/or force-fitting manner.

During embroidering, the carriage 21 is moved from one stitching position to another in rapid succession. The accelerations and changes in direction, occurring in rapid sequences, of the embroidery frame and/or the material holding device 13 and the article 11 stretched therein can lead to undesired oscillations of the embroidery frame 13 interfering with the predetermined target movement. By evaluating the measurement signals of pressure, force, or torque sensors 43, characteristic values can be calculated, which perhaps correspond to a certain phase lag of the mechanical oscillations of the embroidery frame 13.

Alternatively or in addition to the force sensors 43, acceleration sensors 44 could also be used for detecting oscillations at the material holding device 13 and/or other elements mechanically coupled to the material holding device 13 of the embroidery device 1. Preferably, such acceleration sensors 44 are mounted at the material holding device 13 at a distance as great as possible from the second carriage 21 of the driving device 18. Based on the elasticity of the material holding device 13, the greatest oscillation amplitudes can be expected here and the acceleration sensors 44 react most sensitively to these oscillations, here. Ideally, micro-mechanical acceleration sensors 44 are used. They can be produced in very small dimensions and do not hinder the embroidery process. Thanks to the low weight they hardly affect the oscillation behavior of the material holding device in a negative way. Due to the low power consumption it is possible to supply power to such micro-mechanical acceleration sensors 44 via small batteries, so that an electric connection to the driving device 18 and/or to the machine control 9 is not mandatory. Processing the measured signals can directly occur via the integrated sensor chip and the transmission of signals to the control 9 can occur via radio, for example. Of course, conducting connections for the power supply of the sensor 44 and for transmitting signals to the machine control 9 are possible, as well.

The machine control 9 evaluates the measurement signals generated by the sensor(s) 29, 43, 44 and controls or adjusts the movements of the x-y-drive and the sewing needle 23 in a manner that the stitching positions of the sewing needle 23 are equivalent to the predetermined values saved. Here, the oscillations of the frame 13 and/or the article to be sewn 11 are determined and minimized and/or the stitching movements of the sewing needle 23 are temporally optimized, so that the stitching position can coincide as well as possible with the predetermined values even in vibrating frames 13. The material holding device 13 with the article 11 stretched therein is an oscillating system based on the weight and the elasticity of the article 11 to be sewn. It is a component of a complex overall oscillation system, which sequentially comprises the following components: first motor, first transmission, first toothed belt 45, first carriage 19, second motor, second transmission, second toothed belt 45, second carriage 21, material holding device 13, article to be sewn 11. Therefore, the detection of the oscillations of the article to be sewn 11 in the immediate environment of the stitching site of the sewing needle 23 is the method least subjected to incidental or systematic faults.

FIG. 5 shows schematically a control arrangement with an adaptive control 51 for controlling a motor M of the drive device 18. The control 51 can be constructed, e.g., cascade-like. At the input side, the control 51 is fed, on the one side, with target values 53, such as motor rotation or rotation angle of the motor, and, on the other side, the actual or measured dimension 55, such as the motor rotation angle detected by a speed sensor, the position, and the acceleration of the article 11 to be sewn, or the forces determined by the force sensors 43. At the exit side, adjustment values 57, such as stepper-motor switches and phase and power values are forwarded to a power component 58 for controlling the motor M by the adaptive regulator 51.

Structural possibilities and effectiveness of the adaptive regulators are known, for example, from ISBN-3-527-25347-5 “Winfried Opelt: Kleines Handbuch der Regelungstechnik [Small Manual of Control Technology], chapter 65, pages 729-735 (automatic adjustments)”, or from the lectures “Einfuehrung in die adaptive Regelung [Introduction to the Adaptive Control], part I, “Parameteridentifikation” [parameter identification], 2003, by Dr. E. Shafal, Institut fuer Mess- und Regeltechnik of the Eidgenoessische Technische Hochschule.

The control of current phase and switching points and/or the commutation of stepper motors with such adaptive controls is additionally advantageous in that the stepper motors can be operated under overload for a short period of time. Therefore, it is not necessary to size the motors to match individual extraordinary power peaks. In general, smaller and more cost effective stepper motors can be used.

In an advantageous embodiment of the invention, a learning process is provided, by which connections and/or dependencies between certain motion patterns of the x-y-drives and the oscillation behavior of specific configurations of the material device 13 and an article to be sewn 11 are determined.

Depending on the stretched article to be sewn 11, the oscillation behavior can be different. Such learning processes are preferably performed with the sewing needle 23 being raised and inactive. For example, for both drives, certain sequences of alternating movements with one or more different amplitudes can be performed independent from on another and with a series of predetermined oscillating frequencies. When the control 9, based on sensor signals, determines an excessive oscillation of the frame 13 and/or the article to be sewn 11, one or more parameters of the control frequency are varied until the amplitude of the oscillation falls below a predetermined limit. A series of suitable control parameters results depending on the control frequency. In stepper motors, for example, such control parameters are the number of support sites used with the respective predetermined target values for the number of steps per time unit. The control parameters determined in this manner can be saved in a storage unit of the control 9 or in another storage medium.

In a suitable embodiment of the storage unit, different sets of control parameters can be determined and saved for different types of articles to be sewn.

In drives using servomotors, usefully optimized control parameters can be determined.

Learning processes can alternatively occur directly during embroidering as well. Here, it is accepted that slightly higher deviations of the stitching positions from the predetermined target position can occur in individual points of the article to be sewn 11.

List of Reference Characters

-   1 Embroidery device -   3 Sewing machine -   5 Embroidery module -   7 Connection wire -   9 Sewing machine control -   11 Article to be sewn -   13 Material holding device (Embroidery frame) -   15 Fastening means -   17 Holder -   18 Driving device -   19 First carriage -   21 Second carriage -   22 Guiding rod -   23 Sewing needle -   25 Machine head -   27 Needle rod -   29 Optic sensor -   30 Image processing unit -   31 Sewing foot -   32 Sole -   33 Light source -   35 Prism -   37 Lenses -   39 Image sensor -   41 Connection wire -   42 Plug -   43 Force sensor -   44 Acceleration sensor -   45 Toothed belt -   47 Guiding grooves -   48 Fixing device -   49 Holding pin -   51 Adaptive control -   53 Target values -   55 Measurement values -   57 Guiding values -   59 Power component 

1. A method for minimizing stitching faults in embroidering devices (1) which include a material holding device (13) for stretching an article to be sewn (11) and with a driving device (18) for positioning the material holding device (13) in reference to a stitch formation device in order to perform sewing stitches at predetermined target positions, the method comprising: detecting oscillations of the article to be sewn (11) or the material holding device (13).
 2. A method according to claim 1, further comprising: controlling the driving device (18) and/or the stitch formation device depending on the detected oscillations of the article to be sewn (11) or the material holding device (13) and minimizing deviations of actual stitching sites from the corresponding predetermined target positions caused by the oscillations.
 3. A method according to claim 1, further comprising: determining dependencies of motion patterns of the driving device (18) and an oscillation behavior of the article to be sewn (11) stretched in the material holding device (13).
 4. A method according to claim 3, further comprising: saving data in a storage unit, from which dependencies can be deducted between the motion patterns of the driving device (18) and the oscillation behavior of the article to be sewn (11) stretched in the material holding device (13), or from which an optimized control of the driving device (18) can be deducted in that the deviation of the actual stitching sites from the corresponding target values are minimized.
 5. A device for minimizing stitching faults in embroidery devices (1), comprising a material holding device (13) for stretching the article to be sewn (11) and a driving device (18) for positioning the material holding device (13) in reference to a stitch formation device in order to perform sewing stitches at predetermined target positions, and at least one sensor (29, 43, 44) for determining oscillations of at least one of the article to be sewn (11) or the material holding device (13).
 6. A device according to claim 5, wherein the at least one sensor (29, 43, 44) is an optic sensor (29) with a light source (33) and an image sensor (39), with the image sensor (39) being able to detect at least two spatial dimensions for resolution.
 7. A device according to claim 5, wherein the at least one sensor (29, 43, 44) comprises at least one of a pressure sensor, a force sensor, a torque sensor (43) or an acceleration sensor (44).
 8. A device according to claim 7, wherein the at least one sensor (29, 43, 44) comprises a pressure, force, or torque sensor (43) arranged in a connection area of the material holding device (13) to the driving device (18).
 9. A device according to claim 7, wherein the at least one sensor (29, 43, 44) comprises an acceleration sensor (44) arranged at the material holding device (13), located at a distance from a fastening device (15) for attaching the material holding device (13) to the driving device.
 10. A device according to claim 5, wherein an adaptive control (51) is provided for controlling a motor or motors (M) of the driving device. 